Presently, signal lamps are used for front and rear running lights, brake lights, turn indicator lights, backup lights or fog lights in external automobile lighting. An optical system of the signal lamp, typically, includes a light source, a reflector, one or more optical filters, and an exterior lens.
The light sources used are bright incandescent light bulbs or light emitting diodes (LEDs).
Typically, there are two types of optical systems: direct and indirect.
A direct optical system has a visible light source situated approximately in a middle of a reflector. A direction of reflected light is in a direction of an axis of the light source.
On the other hand, indirect optical system has a visible light source situated at a side of a reflector, while a direction of reflected light is approximately perpendicular to an axis of the light source.
A certain portion of light emitted by the light source cannot be effectively reflected and is lost as direct light, thereby decreasing an efficiency of the optical system. Further, the light source can be easily recognized as a relatively bright object against a darker background of a reflecting surface of the reflector.
It would be desirable to produce a signal lamp having a hidden light source, wherein the light source is not visible from any direction, while a light emitting surface of the reflector is sufficiently visible.